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Monthly Archives: May 2017

Using regular gas in an engine that requires premium could void your warranty. That is most likely to happen if using regular causes severe engine knock or pinging (premature ignition of the fuel, also known as detonation) that damages the pistons or other engine parts.

For example, here is what GM says about the subject in an owner’s manual for a vehicle that requires premium:

“Use premium unleaded gasoline with a posted octane rating of 91 or higher. If the octane is less than 91, you could damage the engine and may void your vehicle warranty. If heavy knocking is heard when using gasoline rated at 91 octane or higher, the engine needs service.”

Note that this applies only to engines that require premium gas. Some manufacturers recommend premium gas but say that regular or mid-octane gas can be used instead. They usually warn that using lower-octane gas could reduce performance. When that happens noticeably, or if engine knock occurs, they advise to start using premium.

The computers that manage modern engines are able to adjust the ignition system to accommodate lower-octane gas — to a point. With regular gas, fuel economy and acceleration will likely deteriorate at least slightly. Because regular has lower octane, it is more prone to detonation. Burning regular in an engine designed for premium on a long-term basis or under heavy loads can cause engine knock, and that in turn can damage the pistons, valves or spark plugs. Due to the presence of knock sensors and the car’s ability to retard the spark timing, you might not hear knocking, but that doesn’t mean premium is unnecessary.

If steam is pouring from under your hood, a temperature warning light is glowing bright red on your dashboard or the needle in the temperature gauge is cozying up to the High mark, it’s time to pull off the road and shut down the engine before it fries from overheating.

Any indication of overheating is a serious matter, so the best course of action is to shut down the engine to prevent further damage. Driving a car with an overheated engine can warp cylinder heads and damage internal engine parts such as valves, camshafts and pistons.

Even letting the engine cool for an hour and topping off the radiator with a 50-50 mix of antifreeze and water may not fix what’s wrong. Here are some reasons an engine will overheat:

The coolant level could be extremely low, because of long-term neglect or because a leak has developed in the radiator or radiator hoses. Coolant circulates inside the engine block to cool it, and the leak might be in the block, or from the water pump or heater hoses. Old coolant loses its corrosion-inhibiting properties, allowing rust to form and ultimately causing damage.

The thermostat that allows coolant to circulate may be stuck in the closed position or a clog may have developed, perhaps from debris in the cooling system.

The engine cooling fan has stopped working or the radiator’s cooling fins are clogged with debris so that the air flow that reduces the coolant temperature is restricted.

Several aftermarket manufacturers sell engine air filters that they claim provide better airflow and increase horsepower and acceleration as a result. Some of these companies have many loyal customers who swear that they have benefited, particularly in performance, from using these high-flow filters.

These filters are often made of cotton or nanofibers, and some can be cleaned and lubricated with a special oil and then reused, with at least one brand guaranteeing they will last a million miles. Others can be cleaned with an air hose and reused. Many are designed to directly replace the stock paper air filters provided by the vehicle manufacturers; others are included in a freer-flowing air intake system that delivers more fresh air to the engine.

On the surface, these claims make sense. Engines are like athletes in that the better they can breathe, the faster they can go.

However, independent tests have found that these aftermarket filters may provide little or no performance benefit, and some types allow more dirt into the engine. That dirt will get into the engine oil, and the abrasive effects can damage internal engine parts. In addition, some users say that the oil sprayed on some of these filter types gets into the engines’ air intake systems as well.

The EPA has not tested oil-bathed filters or other free-flow air filters, but it has conducted tests that compared clogged conventional air filters against new ones. The EPA found no significant loss of fuel economy from a clogged air filter but did find in a test of gasoline-powered vehicles that acceleration improved with a clean air filter.

The only guaranteed result of using premium gas in an engine designed for regular is that you will spend more money. As far as any tangible benefits, the chances are slim to none.

If your engine runs fine on regular, filling it with premium is unlikely to boost acceleration or fuel economy by more than insignificant amounts. No matter what you’ve heard, premium won’t do more to clean deposits from your fuel injectors or other parts of the fuel system because today’s regular gas contains the same detergent additives.

The main difference with premium is its higher-octane rating, 91 or higher compared with 87 for regular. The higher octane gives premium gas greater resistance to early fuel ignition, which can result in potential damage, sometimes accompanied by audible engine knocking or pinging. Higher octane allows engines to have higher compression ratios (for a more energetic explosion), more advanced ignition timing or forced-air induction like turbochargers or superchargers. They perform best when fed premium gas.

But if the vehicle manufacturer says your engine needs only 87-octane regular, that is what you should use. The higher octane of premium gas won’t make your car faster. The opposite is possible, because higher-octane gasoline technically has less energy than lower-octane; it’s the fuel’s ability to be compressed more without pre-igniting that results in more power when used in the appropriate engine. Premium gas is not “stronger.”

If you burn premium because you think it makes the engine peppier, that is probably psychological: I’m paying more, so I must be getting more. Some motorists claim they get better fuel economy with premium, but some of that could be due to favorable weather conditions (such as warm weather instead of cold) or other factors.

If you use premium because your engine knocks on regular, you are treating the symptom, not the cause. Something else might be causing the knock, such as carbon deposits or hot spots that should be diagnosed and treated by a mechanic.